1. Field
Embodiments of the present invention relate to an organic light emitting display and a driving method thereof.
2. Description of Related Art
Recently, various flat panel displays with reduced weight and volume in comparison to a cathode ray tube have been developed. The various flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting diode (OLED) display, etc.
Among the various flat panel displays, the organic light emitting display, which displays an image using organic light emitting diodes that emit light by re-combination of electrons and holes, has rapid response speed and low power consumption.
Generally, OLED displays can be classified as a passive matrix type OLED (PMOLED) display or an active matrix type OLED (AMOLED) display according to a method of driving the OLEDs.
The AMOLED display includes a plurality of gate lines, a plurality of data lines, a plurality of power lines, and a plurality of pixels that are coupled to the data lines and the power lines and arranged in a matrix form. Also, each of the pixels generally includes an organic light emitting (EL) device, two transistors, that is, a switching transistor that transfers a data signal and a driving transistor that drives the EL device according to the data signal, and a capacitor that maintains a data voltage corresponding to the data signal.
Such an AMOLED display has a low power consumption, but the intensity or amount of current flowing through the organic light emitting device varies according to deviation in threshold voltage among the transistors, thereby causing display non-uniformity.
In other words, since the characteristics of the transistors provided in each pixel vary according to variables in their manufacturing processes, it is difficult to manufacture the transistors so that the characteristics of all of the transistors in the AMOLED display are identical, thereby causing deviation in the threshold voltage between the transistors of different pixels.
A compensation circuit that includes a plurality of transistors and capacitors may be provided in the respective pixels. However, in this case, each pixel includes the additional plurality of transistors and capacitors of the compensation circuit.
More specifically, if the compensation circuit is added in each pixel as described above, additional transistors, capacitors and signal lines for controlling the transistors are added in each pixel so that in a bottom emission type AMOLED display, the aperture ratio is reduced and probability that defects are generated is increased due to the increased complexity in the constituents of the circuit.
Moreover, there is a recent demand for a high-speed scan driving of 120 Hz or more in order to remove the screen motion blur phenomenon. However, in this case, a charging time available for each scan line is significantly reduced. In other words, when the compensation circuit is provided in each pixel so that additional transistors are provided in each pixel coupled to one scan line, capacitive load of the scan line becomes large. Therefore, a high-speed scan driving is difficult to be implemented.